Broadcast fumigation films have been used in agriculture to confine chemical treatment agents, such as soil fumigants, to the areas where they are applied. Polyethylene materials have been used in the manufacture of such films. Polyethylene films are well suited for such use due to their ability to resist puncturing and tear propagation. However, polyethylene layers can be permeable to volatile gaseous compounds used for soil fumigation such as methyl bromide, chloropicrin, methyl iodide, dimethyl disulfide, and telone, among others. The escape of such fumigation compounds by passing through the broadcast fumigation film is undesirable.
Methyl bromide (MeBr) is an odorless, colorless gas that has been used in agriculture as a soil fumigant to control a wide variety of weeds and pests. However, MeBr is classified as a Class 1 ozone-depleting substance, and so there have been efforts to develop broadcast fumigation films that allow for lower MeBr usage rates per acre by more effectively confining the fumigant during the course of soil treatment.
One type of commercially available broadcast fumigation film is a virtually impermeable film (VIF). Such VIF's typically contain a nylon layer, which is known to have suitable barrier properties. Although commercial VIF's have suitable barrier properties and are not susceptible to barrier loss by weather or soil conditions, they are not as resistant to puncturing and tear propagation as polyethylene mulch films. As a result, nylon multilayer barrier films have had limited use in the agricultural industry despite nylon's suitable barrier properties.
Metalized polyethylene films have also been widely used as broadcast fumigation films. One such film is commercially available from Canslit, Inc., Montreal, Canada. With metalized films, a thin layer of aluminum or other metal is deposited on the film in a vacuum chamber. Such films are primarily polyolefin-based and consequently have excellent resistance to tearing, but their barrier properties are reduced as compared to a film containing a nylon barrier layer. Also, the metal layer can disintegrate or dissolve under a variety of soil and weather conditions. After this happens, the barrier properties of the metalized film are impaired or lost. Because the metalized film is opaque by design, it has the added disadvantage of impairing or preventing the applicator's view of an adhesive applied between adjoining films.
U.S. Patent Application Publication No. 20080044629 discloses mulch barrier films having, for example, a methyl bromide permeability of less than about 15 g/m2-hr and machine direction Elmendorf tear strength of at least about 75 gm. The mulch barrier films are extruded, cast, and preferably embossed, multilayer films having at least one polyolefin layer and at least one polyamide layer.
U.S. Patent Application Publication No. 20080131676 discloses multilayer, microporous breathable barrier films and items such as laminates and garments made from such films. The films contain one or more layers of polymers without fillers in combination with at least two or more microporous breathable layers. The unfilled layers provide a barrier that can effectively allow moisture vapor to pass, but retain fluids and challenge materials.